An electrophotographic image forming apparatus has been widely used, for example, in a copying machine, printer, facsimile device, and multifunctional apparatus, because it is capable of forming a high quality image in an easy operation within a short time, and because its maintenance management is also easy. An electrophotographic image forming apparatus (hereinafter simply referred to as “image forming apparatus”) includes, for example, a photoreceptor, a charging device, an exposure device, a developing device, a transfer device, and a fixing device.
The photoreceptor is a roller member having a surface formed with a photosensitive film. The charging device is for charging the surface of the photoreceptor to a certain electric potential in response to an applied voltage. The exposure device irradiates the charged surface with the light which varies depending on image information so as to form an electrostatic latent image on the charged surface. The developing device provides toner to an electrostatic latent image on the surface of the photoreceptor so as to develop a toner image. The transfer device transfers the toner image on the surface of the photoreceptor to a recording medium (paper).
The fixing device includes, for example, a fixing roller having heating means inside and a pressure roller provided to press against the fixing roller. A recording medium having an unfixed toner image goes through a pressure part between the fixing roller and the pressure roller. This causes the toner image to be fixed to the recoding medium by heat. As a result, an image is printed on the recoding medium.
The developing device includes (i) a developing roller provided to face a rotating photoreceptor on which an electrostatic latent image is formed and (ii) a developer tank which contains developer. The developing roller carries developer inside the developer tank toward the photoreceptor so that an electrostatic latent image on the photoreceptor is developed. In a case where a developer is two-component developer composed of toner and carrier, carrier is left in the developer tank whereas toner is consumed and used for a development of the toner image. A toner supply device supplies another toner to the developing chamber so as to replenish the used amount.
In the developing device with use of two-component developer, it is necessary to mix carrier and toner with a stirring member. The stirring member stirs developer in the developer tank for a certain period of time for charging it to a certain electric potential before carrying out an actual development operation. This is called a preliminary stirring. When the developing device starts carrying out a development operation, the stirring member stirs developer in the developer tank and mixes toner replenished from a toner cartridge and the developer in the developer tank. The developer thus mixed is supplied to the photoreceptor and is used for a development of electrostatic latent image.
Toner is replenished to the developer tank in such a manner that a proper amount of toner is replenished from the toner cartridge to the developer tank at a predetermined timing while a toner supplying port of a toner cartridge and a toner replenishing port of the developing chamber are communicated with each other. In each of the toner supplying port and the toner replenishing port, a shutter is provided. Each of the shutters opens the toner replenishing port and the toner replenishing port when toner is replenished and when a toner cartridge or a developing device is mounted in an image forming apparatus. Whereas, each of the shutters closes the toner supplying port and the toner replenishing port when the developing device is detached from the image forming apparatus so that toner does not leak from either the toner supplying port or the toner replenishing port.
For example, an image forming apparatus in the following patent document 1, a shutter is provided for opening or closing an opening section which is located one end of a toner carrying passage (toner carrying pipe) which causes a toner hopper and a developing device to be communicated with each other. This shutter opens when a developing unit is mounted, and closes when the developing unit is detached.
[Patent Document 1] Japanese Unexamined Patent Publication, Tokukai, 2007-78848 (date of publication: Mar. 29, 2007)
[Patent Document 2] Japanese Unexamined Patent Publication, Tokukaihei, 9-230684 (date of publication: Sep. 5, 1997)
However, in a case of opening or closing the toner carrying passage by using a shutter disclosed in the patent document 1, it is necessary to secure a shelter of the shutter (storage space) while the opening section opens. This causes a problem that space saving of an image forming apparatus is prevented.
On the other hand, in the patent document 2, it is disclosed that a shutter realized by a flexible sheet is provided in a developer replenishing device. The flexible sheet is illustrated in FIG. 11 (a) and FIG. 11 (b). As illustrated in FIGS. 11 (a) and 11 (b), a toner passage hole 110 is provided in part of a flexible sheet 120. FIG. 11 (b) is a cross-section view of the flexible sheet in FIG. 11 (b), viewed along arrows AA.
According to the developer replenishing device, the flexible sheet 120 is moved back and forth (slides) in a direction X so that (i) an opening section for replenishing toner and the toner passage hole 110 overlap each other while toner is replenished and (ii) an area 100 in which the toner passage hole 110 is not formed in the flexible sheet 120 and the opening section for replenishing toner overlap each other while toner is not replenished. This allows toner to be replenished via the opening section which is opened while toner is replenished, and also allows toner not to be replenished because the opening section is closed while toner is not replenished. The flexible sheet 120 becomes compact with ease because of its flexibility. Therefore, it is also possible to save a space for storing the flexible sheet 120, thereby leading in saving space for an image forming apparatus.
As illustrated in FIG. 11 (a), the toner passage hole 110 in the flexible sheet 120 has a rectangular shape defined by opposite sides 110a, which extend in a direction orthogonal to the moving direction X, and opposite sides 110b, which extend in parallel to the moving direction X.
The flexible sheet 120 does not posses an adequate stiffness in thickness direction. Therefore, in a case where the toner passage hole 110 is prepared to have a shape as illustrated in FIG. 11, a peripheral edge of the opposite sides 110a bend in a perpendicular direction with respect to a surface of the flexible sheet as illustrated in FIGS. 12 (a) and (b), in response to pull strength, applied to the flexible sheet 120, causing the flexible sheet 120 to slide in the moving direction X. Note that FIG. 12 (b) is a cross-section view of the flexible sheet 120 in FIG. 12 (a), viewed along arrows BB.
If the flexible sheet 120 slides in a condition illustrated in FIG. 12, the bent part in the flexible sheet 120 gets stuck with an edge of the opening section. As a result, the flexible sheet 120 may fail to slide smoothly.